Silicone products such as silicone fluids, emulsions, sealants, rubber, tubing, etc. are currently being recycled by a catalytic depolymerization process that involves heating the silicone material to convert it into cyclic compounds which are recovered for reuse. This current process employs a batch vessel or batch reactor with heated sidewalls that transfers heat to the mixture therein and elutes, under vacuum, the desired oligomer—a cyclic siloxane.
These current batch operations are limited due to the minimal exposed area from which the oligomer may distill. Utilizing any heated surface above the liquid line requires sufficient agitation to propel material onto this surface. This becomes increasingly less effective as the oligomer elutes and product viscosity increases. Traditionally, this is overcome with the addition of a solvent into which the polymer is dissolved or suspended. Further, the heated surface below the liquid line initiates foaming and carry-over as the oligomer elutes through the increasingly viscous material. Again, the use of a solvent can prevent some carry-over by reducing the viscosity of the material to be recycled. However, the solvent, itself, can distill or carry-over with the desired oligomer requiring subsequent separation. Once the conversion to oligomer is complete, the fill material that remains must be separated from the often expensive solvent.
These current processes are therefore further hindered in that they cannot take the material to dryness in a single distillation step.
The present invention provides improved methods for processing silicone wastes which employ unique agitation to effectively utilize and/or increase the surface area within the reactor. This not only increases efficiency in depolymerization and oligomer recovery but also acts to prevent foaming without the need for solvent, allowing increased distillation rates and improved product put-through as the entire reactor volume is utilized for product alone not product plus solvent.
The present invention also provides a single-pass operation, taking the reactor contents from siloxane material to dry filler and/or catalyst regardless of the viscosity, fill content, or molecular cross-linking of the initial material